Abstract Metabolic syndrome (MetS) is a constellation of risk factors? elevated triglycerides (TG), insufficient high- density lipoprotein cholesterol (HDL-C), elevated blood pressure (BP), elevated fasting blood glucose (FBG), and above-threshold waist circumference (WC)?that is associated with increased cardiovascular disease, type 2 diabetes mellitus, and some forms of cancer. Research suggests that addressing MetS through the workplace could significantly benefit employee health and employer healthcare costs. Habit Design, Inc., has developed an enhanced behavioral health coaching system called Habit Design (HD) that is the first to integrate habit formation, contingency management, and social learning approaches within a smartphone app to support to behavior change in corporate or employee health contexts. In this Fast Track project, we will adapt the HD approach to address MetS. In Phase I, we will 1) refine and extend existing functional prototypes of the HD app to support the latest versions of iOS and Android, 2) conduct usability testing with 8 targeted end users, and 3) prepare standard treatment manuals for the Phase II clinical trial. In Phase II, we will 1) make indicated changes to the HD app based on findings from the Phase I usability test and 2) evaluate the effectiveness of HD coaching compared to standard health coaching in a randomized trial with 424 corporate wellness program participants who have MetS, with follow-up spanning one year. Participants will employees of TriHealth in Cincinnati who have completed a health screening as part of their corporate wellness program and been identified as having at least 3/5 of the following: 1) TG ?150 mg/dL), 2) HDL-C <40 mg/dL in males and <50 mg/dL in females, 3) BP ?130/85 mm Hg, 4) FBG ?100 mg/dl, and 5) WC ?102 cm in males and ?80 cm in females.. All participants will be coached to increase physical activity, which will be monitored with a waist-worn FitBit and Fitabase software. Additionally, participants will choose prior to randomization a goal of increasing fruit and vegetable intake or substituting water for sugar-sweetened beverages. Conditions will be stratified by choice of goal and gender. In both conditions coaching will be monitored for fidelity and delivered in 12 weekly in-person 30-minute sessions followed by one 30-minute maintenance session per month for 4 months. The primary outcome will be average daily step count measured over the course of at least one week at baseline, 4 months, 8 months, and 12 months. The secondary outcome will be standard units increase of fruit/vegetable intake or water intake, according to the participant's choice. Tertiary outcomes will consist of FBG, TG, HDL, BP, WC, and body mass index, measured at each time point. Additionally, we will conduct web-based assessment of self-reported physical activity, junk food, and sugar-sweetened beverage consumption; automaticity of exercise and fruit, vegetable, and water consumption; self-efficacy and social support for target behaviors; and health-related quality of life. Ratings of usability and satisfaction and app usage metrics will be examined. Analyses will be intent-to-treat assuming 15% loss to follow-up.